One of the prerequisites for the development of safe and effective protocols designed to prevent and treat disorders of bone metabolism, growth, and maturation is a thorough understanding of the cell and molecular biology of bone growth and remodeling. Bone development and remodeling involves interactions between bone cells, bone extracellular matrix molecules, the immune system, and systemic factors. Specific cell surface molecules are likely to play important roles in bone cell regulation. However, little is known about the osteoblast and osteoclast cell surface and less is known about plasma membrane modifications during development. Since bone growth and remodeling are dependent on the number and activity of bone resorbing osteoclasts the objective of the proposed studies is to gain additional information on the regulatory mechanisms involved in osteoclast recruitment, differentiation, and action. Specifically, we propose to identify, purify, and biochemically characterize osteoclast-specific cell surface molecules defined by a monoclonal antibody library raised against isolated osteoclasts. Included here is to determine the molecular weights, partial amino acid sequence, and carbohydrate composition of these molecules. Moreover, we plan to determine the functional importance of the osteoclastspecific molecules. In this context we will analyze the response mediated by the interaction between a 96K osteoclast-specific cell surface molecule and its 80K ligand. Functional studies will include monitoring changes in bone resorption activity, cell attachment, phosphorylation, motility, etc. Monoclonal antibodies and oligonucleotide probes generated from known amino acid sequence information will be used to screen an osteoclast cDNA library to identify osteoclastspecific genes. Along with monoclonal antibodies to osteoclasts and their precursors these molecular probes will be employed to trace osteoclast lineage and study osteoclast regulation. We will utilized isolated chick osteoclasts to purify and study osteoclast- specific proteins and determine their function. We have described cell culture systems in which monocyte and marrow nononuclear cells will fuse and form multinucleated giant cells. These cultures will be used to help identify osteoclast precursors. The results from these studies will help understand normal and inflammatory bone loss and aid in devising therapies for arthritic, diabetic, osteoporotic, and periodontal disease associated osteopenia.